Fluids (e.g., oil, water, gas) may exist in a variety of materials, including geologic formations. These fluids are often recovered via a well, or borehole cut into the formation. During exploration and recovery operations, it is useful to determine the caliper and ellipticity of the borehole as an indication of formation stress, compaction, and other mechanisms that operate to deform the borehole. However, rapidly and accurately assessing the caliper and ellipticity of the borehole, especially when the downhole tool acquiring the associated data moves off-center, can be difficult. Thus, improved apparatus, systems, and methods are needed to quickly and reliably determine the caliper and ellipticity of boreholes in geologic formations, under a variety of measurement conditions.